The proposed five-year study will investigate the role of Attention Deficit-Hyperactivity Disorder (ADHD) and other disruptive behaviors, particularly Oppositional Defiant Disorder (ODD) and Conduct Disorder (CD), in the etiology of youth drug involvement, including initiation, maintenance, escalation, and development of psychoactive substance use disorders (PSUD). Drug abuse and ADHD among youth represent vital areas of interest for study because they are highly prevalent in clinic settings, and they are two of the most refractory behavioral disorders of youth. Furthermore, research suggests that rates of drug use and PSUD are significantly greater among ADHD youth compared to non-ADHD youth. The study employs a prospective design to continue to follow community-derived samples of ADHD (n=194), a subgroup of which are considered subthreshold cases, and a demographically-matched nondisruptive comparison group (n=124) for whom both child (T1) and early adolescent (T2) evaluations have been completed. The present study proposes to assess the cohort twice gain during late adolescence (T3) and young adulthood (T4). We have followed these cohorts with the goal of identifying various biopsychosocial predictive and mediating influences, and characterizing their individual, collective and interactive effects, on a range of drug involvement variables (i.e., onset, frequency, quantity, and diagnostic symptoms). Nested within the original longitudinai design was a randomized experiment (initiated at T1 ) that tested the effects of a two year, multicomponent competence enhancement intervention that was designed to promote positive change in several of these mediators. Secondary aims of the proposed study are to evaluate whether the intervention displays any "sleeper" effects on outcome, and, relatedly, to characterize relationships between prior exposure to psychostimulant medication and later outcome.